ObjectiveC Sorting Array

Question

I want to sort array using Bubble Sort. I an missing a small point due to which array is not sorted properly. I would highly appreciate if somebody can figure out the issue.

int i,k;    
int flag = 1;   
MReview *store1 ,*store2,*tempSwap;  
tempSwap = [[MReview alloc] init];  
store1 = [[MReview alloc] init];  
store2 = [[MReview alloc] init];  

for (i = 1;i <= ([arrSortWeeks count]) && flag; i++)
{  
    NSLog(@"Next Iteration: %d", i+1);  
    flag = 0;  
    for (k = 0;   k < ([arrSortWeeks count]-1);   k++)
    {

      store1 = [arrSortWeeks objectAtIndex:k+1];   
      store2 = [arrSortWeeks objectAtIndex:k];  
      //Confronto returns -1 if Store1 is greater and returns 1 if Store1 is smaller
      if (([self confronto:store1.ReviewDate :store2.ReviewDate]) == -1) 
      {    
         tempSwap = store2;  
         store2 = store1;  
         store1 = tempSwap;  
         //[store1 retain];  
         //[store2 retain];  

         [arrSortWeeks replaceObjectAtIndex:k+1 withObject:store1];  
         [arrSortWeeks replaceObjectAtIndex:k withObject:store2];

         flag = 1;  
       }
    }
}

"I want to sort array using Bubble Sort." - that's your first mistake! — Mitch Wheat, Mar 27 '12 at 10:47
Are there any reasons to not use one of the built in sort methods? — Matthias Bauch, Mar 27 '12 at 10:50
@MitchWheat can u plz explain why Bubble sort is not recommended. — Taimur Ajmal, Mar 27 '12 at 10:54
because its worst case complexity is O(N^2). For more than a few thousand items it will take a very, very long time... — Mitch Wheat, Mar 27 '12 at 10:55
@MatthiasBauch .. i'd be glad if you could tell me about built in sort methods. — Taimur Ajmal, Mar 27 '12 at 10:55
Read the documentation for NSArray. There are many methods for sorting. — Mike Weller, Mar 27 '12 at 10:56
@Aadhira .. Question completed now. i used < sign in the code and it removes the rest of the text of my question. — Taimur Ajmal, Mar 27 '12 at 10:56
There is a whole section in the documentation: [Sorting Arrays](http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/Collections/Articles/Arrays.html#//apple_ref/doc/uid/20000132-SW5) — Matthias Bauch, Mar 27 '12 at 10:58
Well I thought Taimur is just practicing some basic algorithms. — Max, Mar 27 '12 at 11:01
FAQ "Be tolerant of others who may not know everything you know." — AnthonyBlake, Mar 27 '12 at 11:09

score 3 · Accepted Answer · edited May 23 '17 at 12:31

If this is for an academic exercise (why else would you use Bubble sort?) then please refer to other posters' responses.

If this is for code to be used in the real world, be aware that Bubble Sort is a very slow sorting method, and not generally recommended for anything beyond a learning tool.

Big O notation is one means of describing the time complexity of sorting algorithms. Bubble Sort's time complexity is O(n²), which means that the time will be a function of the square of the number of elements being sorted, i.e. extremely slow for more than a few elements.

In general, you should be using built-in sort methods wherever possible, as these will have been optimised to sort much more quickly.

This post describes the built-in methods for sorting in iOS, which have the added benefit of being far more concise and readable, as well as being much faster than Bubble Sort.

score 2 · Answer 2 · answered Mar 27 '12 at 11:00

You are iterating your array only ones. BubbleSort needs n^2 iterations to sort your array.

for(int i=0; i< [array count]-2; i++) {
for(int j=1; j< [array count]-1; j++) {
    if([array objectAtIndex:i] > [array objectAtIndex:j]) {
        // SWAP THEM
    }
}
}

The posted code does not exactly fit to what you are doing by i guess you can see what I mean.

score 0 · Answer 3 · edited May 23 '17 at 12:16

0

Instead of removing and adding the objects at particular index, just use the method to replace.

Ex: [arrSortWeeks replaceObjectAtIndex:k+1 withObject:store2];

Also this post will help you how to sort NSMutableArray with custom objects.

edited May 23 '17 at 12:16

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answered Mar 27 '12 at 10:56

KingofBliss

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ObjectiveC Sorting Array

3 Answers3